This application deals generally with apparatus that analyzes analog electrical signals by converting them into digital signals and then displaying them on a cathode ray tube. The analyzer has particular applicability to the diagnosis of internal combustion engines. Most engine analyzers in the marketplace today are of the analog type. A vehicle produces several kinds of electrical signals such as primary and secondary ignition signals which the analyzer displays. In the case of an analog scope, the analog signal wave is processed and applied to the cathode ray tube. The waveform is continuous and therefore continuously matches the electrical signal itself. In a digital analyzer, the analog engine signals are converted into digital information and that digital information is displayed on the cathode ray tube. The waveform can be frozen, that is, the operator can carefully analyze a waveform that was generated at a particular incident of time that has already passed. This capability permits examination of the waveform without the fluctuations or flicker of the waveform that one commonly sees in an analog engine analyzer. The sweep rate for analog engine analyzers varies as a function of engine RPM, so that flicker results particularly at low RPM values. The digital analyzer has a constant sweep rate. Since the sweep rate is independent of variation in engine RPM, flicker of the displayed waveform is eliminated, even at low engine RPM. Also the digital waveform can be stored for future use.
Another advantage of a digital analyzer is that alphanumeric information such as the engine speed, firing voltages, and dwell can be displayed on the screen.
There are digital analyzers in the marketplace today. Also, the prior art does disclose digital analyzers. However, they have certain disadvantages. First they are large, heavy and expensive and must operate from a 120 volt, AC power supply.
Also, the waveforms displayed by prior art digital analyzers consist of a multiplicity of dots. This is not a serious problem when the amplitude of the waveform is constant over time or the rate of change is not great. However, during those portions of the waveform where the fast rise and fall times are present, such as during the firing line of the cylinder, the dots can be widespread making it more difficult to analyze the waveform. Also, when introducing service station operators and others to digital analyzers, it is psychologically important that the waveform appear as similar as possible to the analog waveforms that have been customary on analog analyzers.
The firing line of an ignition signal often requires detailed analysis. However, the firing line normally occurs at the left edge of the CRT screen where it is difficult to study. Prior art digital analyzers do not have the capability of shifting the waveform to the right so that the firing line is more toward the center. Of course, it may be helpful to review the initial portion of waveforms in response to other than ignition signals.
Prior digital analyzers have insufficient capability insofar as measuring the time elapsed between two selected points on a waveform that is being displayed. These prior art analyzers also have relative inflexibility with the alphanumeric and graphic characters that they display.
Because the firing line has such a rapid rise time, it often occurs between two adjacent data sampling points of the analog to digital converter so that the peak display is not completely accurate. Also the approach of prior art digital analyzers in separating the alphanumeric information and the waveform information on the CRT screen is not satisfactory.
Often engine specifications require a waveform of a certain character at a specified engine speed. It is time-consuming and rather difficult for the operator to monitor the change in engine speed so as to be exactly at or nearly at the specified speed and then examine the waveform.
While certain prior art digital analyzers do have the capability of some storage of waveforms for future use, they are unable to save data that has been frozen for any particular waveform and for bar graphs.
Prior art engine analyzers suffer the disadvantage of having the capability of displaying only a single fuel injector waveform at a time, whereas in certain instances, it is desirable to be able to display two or more complete fuel injector waveforms, so that the time between consecutive injector firings can be measured. Prior art analyzers have very substantial memory capability but that adds substantially to their cost. The engine tends to produce extraneous signals which may affect the performance of prior analyzers. Finally, they do not have the capability of expanding a portion of the waveform in order to facilitate analysis.
It is therefore an important object of the invention to provide a means to select the engine speed at which a particular waveform is to be frozen, so that when the engine reaches that speed, the waveform is automatically frozen and can be viewed and examined by the operator.
In accordance with the invention, there is provided an engine analyzer for analyzing an internal combustion engine that produces ignition signals and other engine signals, comprising a cathode ray tube for displaying a waveform corresponding to a selected engine signal which is continuously updated as and when the corresponding electrical signal changes, a keyboard having a key thereon for selecting an RPM set point and additional keys for selecting the magnitude of the RPM set point, microprocessor means coupled to the keyboard and adapted to process the activation of the keys, the microprocessor operating under stored program for (a) determining the time between ignition signals and converting such time into engine speed in RPM. (b) storing the engine speed in RPM thus calculated, (c) determining whether the engine speed in RPM is equal to or greater than the RPM set point, and (d) if so, freezing the waveform on the cathode ray tube to be that corresponding to the electrical signals when the engine speed was at or about the RPM set point irrespective of subsequent changes in the electrical signals.
The invention consists of certain novel features and a combination of elements hereinafter fully described, illustrated in the accompanying drawings, and particularly pointed out in the appended claims, it being understood that various changes in the details may be made without departing from the spirit, or sacrificing any of the advantages of the present invention.